Method of producing a circuit breaker switch

ABSTRACT

CONTACT ELEMENTS FOR A VACUUM CIRCUIT BREAKER ARE MADE FROM A DIFFUSION ALLOY PREPARED BY COATING A COPPER, SILVER OR ALUMINUM BASE STOCK WITH BISMUTH, LEAD, TELLURIUM, INDIUM, THALLIUM OR TIN BY VACUUM DEPOSITION, IMMERSION OR PLATING, AND BY HEATING TIGHTLY PACKED PORTIONS OF THE COATED STOCK TO A TEMPLERATURE BELOW THE MELTING POINT OF THE PRIMARY COMPONENT INA VACUUM OR IN A REDUCING   ATMOSPHERE UNTIL THE COATING MATERIAL DIFFUSES INTO THE BASE TO PRODUCE AN ELECTRODE MATERIAL NOT PREPARED SO SIMPLY TO A REPRODUCIBLE COMPOSITION BY OTHER ALLOYING METHODS.

March 2, 1971 HIROSHI KOBAYASHI ET 3,

7 METHOD OF PRODUCING A CIRCUIT BREAKER SWITCH 2 Sheets-Sheet 1 Filed Feb. 15, 1968 FIGJ.

I'm M K my HB March 2; 1971 HIROSHI KOBAY sl-n ET AL 3,566,463

METHOD OF PRODUCING A CIRCUIT BREAKER SWITCH Filed Feb. 15. 1968 2 Sheets-Sheet 2 WEIIIUQ- United States Patent 01 fice 3,566,463 METHOD OF PRODUCING A CIRCUIT BREAKER SWITCH Hiroshi Kobayashi and Eiji Fujimoto, Tokyo, Japan, as-

signors to Meidensha Electric Mfg. Co., Ltd., Tokyo, Japan Filed Feb. 15, 1968, Ser. No. 705,822 Claims priority, application Japan, Dec. 20, 1967, 42/ 82,085 Int. Cl. H01h 11/00 US. Cl. 29622 9 Claims ABSTRACT OF THE DISCLOSURE Contact elements for a vacuum circuit breaker are made from a diffusion alloy prepared by coating a copper, silver or aluminum base stock with bismuth, lead, tellurium, indium, thallium or tin by vacuum deposition, immersion or plating, and by heating tightly packed portions of the coated stock to a temperature below the melting point of the primary component in a vacuum or in a reducing atmosphere until the coating material diffuses into the base to produce an electrode material not prepared so simply to a reproducible composition by other alloying methods.

The invention relates to electrodes suitable for vacuum circuit breakers, and particularly to a method of producing such electrodes.

It is known to make breaker electrodes from alloys consisting primarily of a metal of good electrical conductivity such as copper, silver or aluminum, and of bismuth, lead, tellurium, indium and the like as a secondary component. The known copper-bismuth, copper-lead, copper-tellurium, copper-thallium, aluminum-bismuth, aluminum-lead, aluminum-indium, aluminum-tin, silver-tellurium and like alloys contain the secondary components in preferred amounts of less than However, the solid solubility of bismuth in copper is only 0.01% at 800 C., and that of lead in copper only 0.29% above 600 C. The solid solubilities of tellurium and thallium in copper, the solid solubilities of bismuth, lead, indium and tin in aluminum, and the solid solubility of tellurium in silver are similarly low. It has therefore been difiicult to produce the alloys by vacuum melting and other conventional processes.

For example, copper and bismuth must be molten at temperatures above 1100 C. to form an alloy. At an assumed melting temperature of 1200 C., the vapor pressure of copper is 3x10 mm. Hg and that of bismuth is 3 1O mm. Hg. so that much more bismuth than copper is lost from the melt by evaporation, making it difficult to hold the proportion of the components in the alloy constant. Bismuth also tends to cause bumping of the melt from which cavities in the alloy may result. Similar difliculties are encountered in alloys of copper with lead, tellurium or thallium in which the solubility of the secondary component is low and the melting points of the two components differ greatly.

Vacuum breakers may require contact elements or electrodes degassed to a state of high purity. It has been customary heretofore to purify the individual components by zone melting or melting in an electron beam, and to alloy them thereafter by electron beam melting or high frequency melting which are subject to the difiiculties outlined above.

Patented Mar. 2, 1971 It is a principal object of this invention to produce contact elements suitable for a vacuum circuit breaker while avoiding the above difficulties.

According to the method of the invention, the secondary alloying component is deposited on stock of the conductive primary component by vacuum deposition, immersion or plating, portions of the coated stock are tightly packed, and the packed material is heated to a temperature below the melting point of the primary component in a vacuum or in a reducing atmosphere until the desired contact material is obtained.

Binary alloy electrode materials capable of being prepared by this method include those of copper with bismuth, lead, tellurium, thallium, of aluminum with bis muth, lead, indium and tin, silver with tellurium, and the like. The resistance of the contact element ultimately produced to bonding by diffusion may be improved by adding a small amount of a refractory ingredient to the principal component, such as tantalum, tungsten, protactinium, technetium, ruthenium, molybdenum, carbon, iridium, osmium, tungsten carbide, tantalum carbide, vanadium, carbide, silicon carbide or zirconium carbide. When electrodes of very high purity are required, the metal constituting the primary component may be purified by degassing in a vacuum or a reducing atmosphere prior to applying the secondary alloying component.

Other objects and advantages of this invention will become apparent from consideration of the following description of preferred embodiments when taken in conjunction with the accompanying drawing in which:

FIG. 1 shows a circuit breaker equipped with electrodes prepared according to the method of the invention in elevational section;

FIG. 2 is a perspective view of an electrode element for use in the apparatus of FIG. 1 on a larger scale, a portion of the element being broken away to better reveal internal structure;

FIG. 3 shows an assembly of elements as seen in FIG. 2 in an intermediate stage of electrode production and in elevational section;

FIG. 4 shows another electrode element in the manner of FIG. 2;

FIG. 5 illustrates an unfinished electrode assembly including elements of the type shown in FIG. 4 in a view corresponding to that of FIG. 3;

FIG. 6 shows degassing apparatus for preparing the element of FIG. 4 in partly diagrammatic representation;

FIG. 7 illustrates coating apparatus for securing the secondary alloying element to the surface of a primary component in the method of the invention, the view being in partly diagrammatic elevation;

FIG. 8A shows an electrode assembly similar to that of FIG. 5 in the finished condition in plan view; and

FIG. 8B illustrates the device of FIG. 8A in elevational section.

The vacuum circuit breaker of FIG. 1, not in itself part of this invention, has a stationary upper electrode 1 supported on a rod 1 and a movable lower counterelectrode 2 on a similar rod 2 sealed by steel bellows 3 to the metallic bottom plate 7 which downwardly closes the insulating, outer casing 5 of the breaker. A metal cylinder 4 envelops the electrodes 1, 2 to shield the insulating casing 5 against metal deposition from an are between the electrodes. The rod 1 is fastened to a metallic top plate 6 on the casing 5. The sealed cavity 3 8 in the casing is evacuated to a pressure of 10- to mm. Hg.

The method of the invention for producing the electrodes 1, 2 will now be explained with reference to a binary copper-bismuth alloy.

Copper sheet stock 0.125 mm. thick and 10 mm. wide is prepared by vacuum melting, degreased, pickled, rinsed with water and washed with alcohol. It is then coated with 1% (by weight) bismuth by thermal evaporation in a vacuum of 10 to 10- mm. Hg to produce the element 11 shown in 'FIG. 2 which consists of a copper sheet 9 carrying a bismuth coating 10 of uniform thickness on one of its major faces. Several such elements are stacked in a copper jig or holder 12 in which they are packed tightly by clamping or brazing as shown in FIG. 3.

The assembly seen in FIG. 3 is held at 750 C. for 60 minutes in a reducing atmosphere of pure hydrogen gas so that the bismuth diffuses into the copper sheet material. The resulting contact material contains 0.2% bismuth, 80% of the bismuth originally present in the form of a surface coating being lost by evaporation.

The electrodes ultimately produced have been found to perform satisfactorily for cutting off current of 6.25 kv. and 6 ka.

For electrodes of high purity, the copper stock is purified by degassing, the time required being short because of the thinness of the material, and capable of being further shortened by raising the degassing temperature.

Alternatively, contact elements are made from copper Wire 0.5 mm. thick and formed by vacuum melting with or without refractory ingredient. The wire is degreased, pickled, rinsed with water, washed with alcohol and coated with 2% (by weight) bismuth by thermal evaporation in a vacuum of 10' to l0 mm. Hg. The resulting electrode element 11' is shown in FIG. 4 and consists of a copper core 9' carrying a thin bismuth coating 10'. Several elements 11' are bunched together and clamped or brazed in a jig 12' as shown in FIG. 5. They may also be twisted together, if desired, into a multiplestrand cable of 20 mm. overall diameter, and sections of the cable mm. long, may be inserted in the jig 12.

Bismuth is diffused into the copper core at 750 C. in 60 minutes in a pure hydrogen atmosphere or other reducing atmosphere. The contact material so obtained contains 0.3% bismuth, 85% of the originally present bismuth being lost by evaporation. The electrodes formed have been found to perform satisfactorily in interrupting current of 6.25 kv. and 6 ka.

If so required, the thin copper wire is readily degassed prior to application of the bismuth coating as described above, and the degassing time may be reduced by operation at an elevated temperature not exceeding the melting point of the metal.

A lead-copper alloy electrode meeting requirements for high purity is prepared as follows:

A band of copper sheet stock 0.25 mm. thick and 100 mm. wide and formed by vacuum melting is degreased, pickled, rinsed in water and washed with alcohol. It is then degassed for 60 minutes at 1050 C. in an atmosphere of pure hydrogen. It is thereafter coated with 1% lead by thermal evaporation, as described above. Several elements of lead coated copper are then coiled, and the coil is secured in a jig as described above. Lead is diffused into the copper at 800 C. within 60 minutes in a pure hydrogen atmosphere. The contact material so obtained contains 0.9% lead, having lost 10% of the originally present lead by evaporation. Electrodes made from the material were tested successfully at 6.25 kv. and 12 ka.

A copper-lead electrode material is also prepared from copper wire 9, 0.5 mm. thick, which is degreased, pickled, rinsed in Water, washed with alcohol and degassed in the apparatus shown in FIG. 6 by passage through a 75 furnace 13 in which an atmosphere of pure hydrogen gas (dew point 60 to C.) is maintained. The furnace temperature is 1050 C. and the dwell time 20 minutes. The wire 9' is drawn from a supply coil 14 and wound on a take-up roll 15 after degassing. Entry of air into the furnace with the wire is prevented by flame curtains 16, and cooling jackets 17 maintain a low wire temperature outside the furnace 13. Nipples 18a, 18b on the furnace admit and discharge the hydrogen. The furnace is heated by a coil 19. The Wire is moved through the furnace by rollers 20 and by a motor 21.

The degassed copper wire 9' is coated with lead in the immersion apparatus 22 shown in FIG. 7. It has a chamber 23 which is evacuated to 10" to 10 mm. Hg by a pump (not shown) connected to a nipple 29 on the chamber 23. A tank 24 in the chamber 23 is filled with lead kept in the liquid state by a coil 27 which is energized by an electric current source 28. The degassed wire is drawn from a supply coil 25 in the chamber, passes through the molten lead, and is thereby coated with a 1% lead deposit 10 to form an electrode element 11 which is wound on a take-up coil 26.

A twisted cable made from the coated wire as described above is held in a jig at 800 C. for 60 minutes in a hydrogen atmosphere to diffuse lead into the copper, and to form an electrode material containing 0.9% lead, 10% of the originally present lead being lost by evaporation. The electrodes so produced were found effective at 6.25 kv. and 12 ka.

An electrode made from wires of varying diameters is shown in FIGS. 8A and 8B. Prior to the diffusion treatment, the thinner Wires are arranged in the center of a bundle of wires and enveloped by circular rows of Wires gradually increasing in diameter.

The method of the invention permits the ratio of the components in the electrode material to be varied as desired by varying the amount of second alloying material in the deposited coating. Alloys not readily formed by melting processes are conveniently prepared by diffusion. The primary component of the alloy may readily be degassed prior to the coating process.

What we claim is:

1. method of assembling a contact breaker which comprises:

(a) coating stock of a conductive metal selected from the group consisting of copper, silver, and aluminum with a thin layer of an alloying component selected from the group consisting of bismuth, lead, tellurium, indium, thallium, and tin;

(b) tightly packing a plurality of portions of said coated stock;

(c) holding said packed portions at an elevated temperature lower than the melting point of said conductive metal until said alloying component diffuses into said conductive metal;

(d) fixedly fastening said packed portions in a conductive holder to constitute an electrode;

(e) assembling said electrode in a common casing with a counterelectrode for relative movement of said electrode and said counterelectrode toward and away from a position in which an arc may pass between said packed portions and said counterelectrode When a voltage is applied to the same.

2. A method as set forth in claim 1, wherein said conductive metal, prior to said coating, is held in a vacuum or a reducing atmosphere at an elevated temperature below the melting point thereof until said metal is purified by degassing.

3. A method as set forth in claim 1, wherein said stock is sheet stock.

4. A method as set forth in claim 3, wherein said portions of said stock are being stacked for packing the same.

5. A method as set forth in claim 3, wherein said portions of said stock are coiled for packing the same.

6. A method as set forth in claim 1, wherein said stock is wire shaped.

7. A method as set forth in claim 6, wherein said portions of said stock are bunched for packing the same.

8. A method as set forth in claim 5, wherein said portions of said stock are twisted into a cable for packing the same.

9. A method as set forth in claim 1, wherein said elevated temperature is higher than the melting point of said alloying component.

References Cited UNITED STATES PATENTS 6 2,379,232 6/1945 Hensel 29630X 3,091,026 5/1963 Hill et a1. 29471.1X 3,131,469 5/1964 Glaze. 3,029,496 4/1962 Levi 29419X 3,254,189 5/1966 Evanicsko, Jr., et al. 29630X 2,253,401 8/1941 Slepian 20066 2,434,305 1/1948 Wise 200166X 3,443,304 5/1969 Maier 29472.3X

JOHN F. CAMPBELL, Primary Examiner R. W. CHURCH, Assistant Examiner U.S. Cl. X.R. 

